Heat-treated material with improved mechanical properties

ABSTRACT

A material includes a transparent substrate coated with a stack of thin layers including at least one silver-based functional metallic layer, at least one blocking layer located directly in contact with a silver-based functional metallic layer, and at least one zinc-based metallic layer located above or below this silver-based functional metallic layer, directly in contact or separated by one or more layers having a total thickness of less than or equal to 20 nm.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Stage of PCT/FR2019/052716, filed Nov. 15, 2019, which in turn claims priority to French patent application number 1860583 filed Nov. 16, 2018. The content of these applications are incorporated herein by reference in their entireties.

The invention relates to a material comprising a transparent substrate coated with a stack of thin layers comprising at least one silver-based functional metallic layer. The invention also relates to glazings comprising these materials and also to the use of such materials for manufacturing thermal insulation and/or solar protection glazings.

Silver-based functional metallic layers (or silver layers) have advantageous properties of electrical conduction and of reflection of infrared (IR) radiation, hence their use in “solar control” glazings, targeted at reducing the amount of incoming solar energy, and/or in “low-emissivity” glazings, targeted at reducing the amount of energy dissipated toward the outside of a building or of a vehicle.

These silver layers are deposited between coatings based on dielectric materials generally comprising several dielectric layers (hereinafter “dielectric coatings”) making it possible to adjust the optical properties of the stack. These dielectric layers additionally make it possible to protect the silver layer from chemical or mechanical attacks.

The optical and electrical properties of the materials depend directly on the quality of the silver layers, such as their crystalline state, their homogeneity and also their environment. The term “environment” is understood to mean the nature of the layers close to the silver layer and the surface roughness of the interfaces with these layers.

In order to improve the quality of silver-based functional metallic layers, it is known to use dielectric coatings comprising dielectric layers having a stabilizing function which are intended to promote the wetting and the nucleation of the silver layer. Crystallized zinc oxide-based dielectric layers are used in particular for this purpose. This is because the zinc oxide deposited by the cathode sputtering process crystallises without requiring additional heat treatment. The zinc oxide-based layer can thus serve as an epitaxial growth layer for the silver layer.

With this same objective, it is also known to use blocking layers located between a functional layer and a dielectric coating, these blocking layers having the function of protecting these functional layers from possible degradation during deposition of the upper dielectric coating and/or during a heat treatment. Numerous possibilities, varying in particular in the nature, the number and the position of said blocking layers, have been proposed.

The invention relates very particularly to stacks which have to undergo a high-temperature heat treatment, such as an annealing, a bending and/or a tempering.

In general, high-temperature heat treatments are liable to make the stacks more sensitive to scratches. Furthermore, when scratches are created in a material before heat treatment, they become considerably more visible after heat treatment.

The applicant has observed that stacks comprising, close to a silver layer, both blocking layers chosen from certain materials and/or having certain thicknesses and dielectric layers comprising zinc, in particular based on zinc oxide or based on zinc tin oxide, following the heat treatment advantageously exhibit improved scratch resistance properties, and disadvantageously exhibit deteriorated resistivity.

These phenomena appear partly linked to changes within the silver layer induced by the migration of species during the heat treatment. These changes impact not only the visual appearance but also the optical properties and the electrical conductivity of the stack.

The reasons for and mechanisms of the species migration are still poorly understood. Their occurrence appears to be strongly dependent on the nature of the blocking layers and of the dielectric layers constituting the dielectric coatings located close to the silver layer. The presence of certain dielectric materials in the stack, in particular of certain oxides, or of certain blocking layers, promotes the migration of certain species, in particular the release of metallic zinc elements close to the silver layer, via the reduction of the dielectric layers comprising zinc.

The improvement in the scratch resistance could be due to the doping of the silver layer with zinc.

The deterioration of the resistivity could be due to the presence of metallic zinc elements or due to zinc-related defects located at the upper or lower interface of the silver layer and/or at the grain boundaries of the silver layer.

The presence of metallic zinc elements in the silver layer appears to make it possible to improve durability at the expense of resistivity.

On the basis of this observation, the applicant is interested in the effects of intentionally inserting a zinc-based metallic layer into stacks which are fragile from the point of view of scratch resistance and are intended to undergo a heat treatment. The objective is to obtain, by directly adding the metallic zinc elements, the positive effect on scratch resistance. By proceeding in this way, the improvement no longer depends on the creation of mobile species of metallic zinc by reduction of the layer comprising zinc.

The applicant has thus surprisingly discovered that the joint presence of a zinc-based metallic layer and a blocking layer close to the silver layer makes it possible not only to significantly improve the scratch resistance of the silver stacks but also to drastically reduce hot corrosion and cold corrosion in humid environments.

The invention thus relates to a material comprising a transparent substrate coated with a stack of thin layers comprising at least one silver-based functional metallic layer and at least two dielectric coatings, each dielectric coating including at least one dielectric layer, so that each functional metallic layer is disposed between two dielectric coatings, characterized in that the stack comprises:

-   -   at least one blocking layer, in particular a blocking overlayer         and/or underlayer, located directly in contact with a         silver-based functional metallic layer, chosen from metallic         layers based on a metal or on a metal alloy, metal nitride         layers, metal oxide layers and metal oxynitride layers of one or         more elements chosen from titanium, nickel, chromium, tantalum         and niobium,     -   at least one zinc-based metallic layer, located above or below         this silver-based functional metallic layer, directly in contact         or separated by one or more layers having a total thickness of         less than or equal to 20 nm.

The zinc-based metallic layer is situated in a dielectric coating in contact with said silver-based functional metallic layer. This means that the zinc-based metallic layer is not separated from said silver-based functional metallic layer by another silver-based functional metallic layer.

The presence of a metallic zinc layer close to the silver layer causes, during the heat treatment, the migration of metallic zinc elements into the silver layer following the heat treatment.

The presence of a blocking layer in contact with the silver layer appears to make it possible to slow the diffusion of the metallic zinc through the silver layer and hence to keep the metallic zinc elements in contact with the silver layer, that is to say at the grain boundaries or at the interfaces, for longer.

The migration of metallic zinc elements into the silver layer following the heat treatment makes it possible to improve the scratch resistance after heat treatment regardless of the structure of the stack. The zinc-based metallic layer thus makes it possible to improve the mechanical strength.

A blocking layer located above a silver-based functional metallic layer is called a blocking overlayer. A blocking layer located below a silver-based functional metallic layer is called a blocking underlayer.

An explanation of the beneficial effect associated with the presence of a blocking overlayer or of a blocking underlayer close to the silver layer is as follows.

The silver layers are polycrystalline layers, that is to say composed of a plurality of monocrystalline silver grains. During the heat treatment, a rearrangement takes place which results in a decrease in the number of grains and an increase in the size of the grains.

It is possible that the metallic zinc species diffuse very efficiently into the stack, that is to say at temperatures lower than the temperatures at which this rearrangement occurs.

The case where the zinc-based metallic layer is located above the silver layer is considered. If the metallic zinc elements diffuse at these lower temperatures in the absence of a blocking overlayer, they could easily pass through the silver layer without being sufficiently retained. In this case, the effect on the modification of the mechanical properties and resistivity would be smaller.

However, when a blocking overlay is inserted between the silver and zinc layers, the blocking layer could act as a barrier and slow down the diffusion of the metallic zinc elements. This would make it possible to retain the metallic zinc elements in the silver layer when the higher rearrangement temperatures of the silver layer are reached. The metallic zinc elements would then be retained close to the silver layer. This would explain the significant impact of the presence of the blocking layer on the mechanical properties and on the resistivity.

To a lesser extent, the use of a blocking underlayer also performs the function of preventing the diffusion of the metallic zinc elements and of confining them close to the silver layer. Configurations according to this embodiment can be advantageous.

In this type of stack, that is to say in stacks comprising blocking underlayers, the deterioration in the resistivity is lower and the absorption is generally less critical. In addition, the absorption can be more easily regulated by adjusting the thicknesses of the blocking layers or the thicknesses of the metallic zinc layers.

According to particularly advantageous embodiments, the stacks comprise, close to a silver layer, the combination of a zinc-based metallic layer and a blocking underlayer.

The invention thus makes it possible to develop a material comprising a substrate coated with a stack comprising at least one silver-based functional layer exhibiting, following a heat treatment of bending, tempering or annealing type:

-   -   a lower scratchability and     -   a significantly improved resistance to hot and cold corrosion.

However, without further optimization, these improvements imparted on the stacks are accompanied by a deterioration in the resistivity and the absorption.

The present invention is therefore more particularly suitable for applications in which:

-   -   the obtaining of a low emissivity is not critical and/or     -   an increase in the absorption is likewise not critical or can be         compensated by other means such as a decrease in the thickness         of the blocking layers or a decrease in the absorption induced         by “more” absorbent layers located at any position in the stack.

The solution of the invention is very particularly suitable in the case of stacks having a number of silver-based functional layers, in particular stacks having two or three functional layers which are particularly fragile from the point of view of scratches.

The present invention is also very particularly suitable in the case of stacks with a single silver-based functional layer which are intended for applications in which the stacks are highly subject to cold corrosion in a humid environment. This is in particular the case of single glazing comprising stacks with a single silver layer which are used as glazing for refrigerator doors.

The invention also relates to:

-   -   a glazing comprising a material according to the invention,     -   a glazing comprising a material according to the invention         fitted on a vehicle or on a building, and     -   the process for preparing a material or a glazing according to         the invention,     -   the use of a glazing according to the invention as solar control         and/or low-emissivity glazing for the construction industry or         vehicles,     -   a building, a vehicle or a device comprising a glazing according         to the invention.

Throughout the description, the substrate according to the invention is regarded as being positioned horizontally. The stack of thin layers is deposited above the substrate. The meaning of the expressions “above” and “below” and “lower” and “upper” is to be considered with respect to this orientation. Unless specifically stipulated, the expressions “above” and “below” do not necessarily mean that two layers and/or coatings are positioned in contact with one another. When it is specified that a layer is deposited “in contact” with another layer or with a coating, this means that there cannot be one (or more) layer(s) inserted between these two layers (or layer and coating).

All the light characteristics described are obtained according to the principles and methods of the European standard EN 410 relating to the determination of the light and solar characteristics of the glazings used in the glass for the construction industry.

A glazing for the construction industry generally delimits two spaces: a space described as “exterior” and a space described as “interior”. It is considered that the sunlight entering a building goes from the exterior toward the interior.

According to the invention, the light characteristics are measured according to the D65 illuminant at 2° perpendicularly to the material fitted in a double glazing:

-   -   LT corresponds to the light transmission in the visible region         in %,     -   Rext corresponds to the external light reflection in the visible         region in %, with the observer on the external space side,     -   Rint corresponds to the internal light reflection in the visible         region in %, with the observer on the internal space side,     -   a*T and b*T correspond to the colors in transmission a* and b*         in the L*a*b* system,     -   a*Rext and b*Rext correspond to the colors in reflection a* and         b* in the L*a*b* system, with the observer on the external space         side,     -   a*Rint and b*Rint correspond to the colors in reflection a* and         b* in the L*a*b* system, with the observer on the internal space         side,

The preferred characteristics which appear in the continuation of the description are applicable both to the material according to the invention and, if appropriate, to the glazing or to the process according to the invention.

The stack is deposited by magnetic-field-assisted cathode sputtering (magnetron process). According to this advantageous embodiment, all of the layers of the stack are deposited by magnetic-field-assisted cathode sputtering.

Unless otherwise indicated, the thicknesses mentioned in the present document are physical thicknesses and the layers are thin layers. The term “thin layer” is intended to mean a layer having a thickness of between 0.1 nm and 100 micrometers.

In the following paragraphs, these zinc-based metallic layers are defined as they are obtained during the deposition, that is to say before heat treatment. Insofar as the heat treatment induces the migration of metallic zinc elements into the stack, it is not possible to determine with certainty, according to the deposited thicknesses, how this metallic zinc layer is modified following the heat treatment.

The term “metallic layer” is understood to mean a layer not comprising more than 30%, 20% or 10% of oxygen and/or nitrogen as atomic percent in the layer.

The layers are deposited in metallic form. Following the deposition and before heat treatment, they should not contain more than 10% of oxygen and/or nitrogen. However, depending on the nature of the layer deposited directly above, these zinc-based metallic layers are liable to undergo partial oxidation possibly leading to higher proportions of oxygen or nitrogen. These proportions are however less than 30% or 20%. In any case, at least a portion of the thickness of these zinc-based metallic layers is not oxidized or nitrided.

The zinc-based metallic layers (before heat treatment) comprise at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99% or 100% by weight of zinc relative to the weight of the zinc-based metallic layer.

The zinc-based metallic layers may be chosen from:

-   -   metallic zinc layers,     -   metallic doped zinc layers,     -   zinc alloy-based metallic layers.

According to the invention, the term “metallic zinc layer” is understood to mean metallic layers of pure zinc which may nevertheless comprise some impurities. In this case, the total weight of zinc represents at least 99% by weight of the weight of the zinc-based metallic layer.

According to the invention, the doped zinc layers comprise at least 90.0%, at least 95%, at least 96%, at least 97%, at least 98% or at least 99% by weight of zinc of the weight of the zinc-based metallic layer.

The doped zinc layers may be chosen from the layers based on zinc and on at least one element chosen from titanium, nickel, aluminum, tin, niobium, chromium, magnesium, copper, silicon, silver or gold.

According to the invention, the zinc alloy-based layers comprise at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80% or at least 90% by weight of zinc of the weight of the zinc-based metallic layer.

The zinc alloy-based layers can be chosen from layers based on zinc and on at least one element chosen from titanium, nickel, chromium and tin. By way of example, mention may be made of binary alloys of zinc and titanium such as Zn₂Ti or ternary alloys based on zinc, nickel and chromium such as ZnNiCr.

The thickness of the zinc-based metallic layer is from 0.2 to 10 nm.

The thickness of the zinc-based metallic layer can be:

-   -   greater than or equal to 0.2 nm, greater than or equal to 0.5         nm, greater than or equal to 1.0 nm, greater than or equal to         1.2 nm or greater than or equal to 1.5 nm, or greater than or         equal to 2 nm and/or     -   less than or equal to 10 nm, less than or equal to 8 nm, less         than or equal to 7 nm, less than or equal to 6 nm, less than or         equal to 5 nm or less than or equal to 4 nm.

Preferably, the zinc-based metallic layer or layers is/are located above the silver-based functional metallic layer.

The stack can comprise at least one blocking overlayer, preferably located directly in contact with the silver-based functional metallic layer.

The stack can comprise at least one blocking underlayer, preferably located directly in contact with the silver-based functional metallic layer.

The blocking layers are chosen from metallic layers based on a metal or on a metal alloy, metal nitride layers, metal oxide layers and metal oxynitride layers of one or more elements chosen from titanium, nickel, chromium, tantalum and niobium, such as Ti, TiN, TiOx, Nb, NbN, Ni, NiN, Cr, CrN, NiCr or NiCrN.

When these blocking layers are deposited in the metal, nitride or oxynitride form, these layers can undergo a partial or complete oxidation according to their thickness and the nature of the layers which frame them, for example, during the deposition of the following layer or by oxidation in contact with the underlying layer.

The blocking layers can be chosen from metallic layers, in particular layers of an alloy of nickel and of chromium (NiCr) or of titanium.

Advantageously, the blocking layers are nickel-based metallic layers. The nickel-based metallic blocking layers (before heat treatment) can comprise at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99% or 100% by weight of nickel relative to the weight of the nickel-based metallic layer.

The nickel-based metallic layers may be chosen from:

-   -   metallic nickel layers,     -   metallic doped nickel layers,     -   nickel alloy-based metallic layers.

The nickel alloy-based metallic layers can be based on an alloy of nickel and of chromium.

Each blocking layer has a thickness of between 0.1 and 5.0 nm. The thickness of these blocking layers can be:

-   -   at least 0.1 nm, at least 0.2 nm, at least 0.5 nm, and/or     -   at most 5.0 nm, at most 4.0 nm, at most 3.0 nm, at most 2.0 nm.

In advantageous embodiments, the stack also comprises one or more crystallized dielectric layers located close to the silver layer. These crystallized dielectric layers are generally layers based on zinc oxide.

It appears that the crystallized layers do not prevent the migration of the metallic zinc elements. On the other hand, the presence of these layers slows this migration simply because of their thickness. Preferably, zinc-based metallic layers are separated from the silver layer by blocking layers and/or crystallized layers.

Preferably, the zinc-based metallic layer or layers is/are located above a silver layer and above a blocking overlayer. In this configuration, the zinc-based metallic layer is located above the silver-based functional metallic layer and is separated from this layer by at least one blocking overlayer.

However, other configurations are possible.

The zinc-based metallic layer can be located:

-   -   above a silver-based functional metallic layer, the metallic         zinc layer is in contact with the silver-based functional         metallic layer (Ag/Zn sequence),     -   above a silver-based functional metallic layer, the metallic         zinc layer is separated from the silver-based functional         metallic layer by at least one blocking overlayer (Ag/blocking         layer/Zn sequence),     -   above a silver-based functional metallic layer and below and in         contact with a crystallized dielectric layer, the metallic zinc         layer is in contact with the silver-based functional metallic         layer (Ag/Zn/crystallized layer sequence),     -   above a silver-based functional metallic layer and below and in         contact with a crystallized dielectric layer, the metallic zinc         layer is separated from the silver-based functional metallic         layer by at least one blocking overlayer (Ag/blocking         layer/Zn/crystallized layer sequence),     -   above a silver-based functional metallic layer and above and in         contact with a crystallized dielectric layer, the crystallized         dielectric layer is optionally separated from the silver-based         functional metallic layer by at least one blocking overlayer         (Ag/optionally blocking layer/crystallized layer/Zn sequence),     -   below a silver-based functional metallic layer, the metallic         zinc layer is in contact with the silver-based functional         metallic layer (Zn/Ag sequence),     -   below a silver-based functional metallic layer, the metallic         zinc layer is separated from the silver-based functional         metallic layer by at least one blocking underlayer (Zn/blocking         layer/Ag sequence),     -   below a silver-based functional metallic layer and above and in         contact with a crystallized dielectric layer, the metallic zinc         layer is in contact with the silver-based functional metallic         layer (crystallized layer/Zn/Ag sequence),     -   below a silver-based functional metallic layer and above and in         contact with a crystallized dielectric layer, the metallic zinc         layer is separated from the silver-based functional metallic         layer by at least one blocking underlayer (crystallized         layer/Zn/blocking layer/Ag sequence),     -   below a silver-based functional metallic layer and below and in         contact with a crystallized dielectric layer, the crystallized         dielectric layer is in contact with or separated from the         silver-based functional metallic layer by at least one blocking         underlayer (Zn/crystallized layer/optionally blocking layer/Ag         sequence).

The physical thickness of all the layers separating the silver-based functional metallic layer from the zinc-based metallic layer can be between 0 and 15.0 nm, or between 0 and 10 nm, or between 0 and 5 nm, between 0.2 and 5 nm, between 0.5 and 3 nm, between 0.8 and 1.5 nm.

The thickness of all the layers separating the silver-based functional metallic layer from the zinc-based metallic layer can be:

-   -   greater than or equal to 0.2 nm, greater than or equal to 0.4         nm, greater than or equal to 0.5 nm, greater than or equal to 1         nm, greater than or equal to 2 nm, greater than or equal to 3         nm, greater than or equal to 4 nm, greater than or equal to 5         nm, greater than or equal to 6 nm, greater than or equal to 7         nm, greater than or equal to 8 nm or greater than or equal to 9         nm and/or     -   less than or equal to 20 nm, less than or equal to 15 nm, less         than or equal to 13 nm, less than or equal to 12 nm, less than         or equal to 11 nm, less than or equal to 10 nm, less than or         equal to 9 nm or less than or equal to 8 nm, less than or equal         to 7 nm, less than or equal to 6 nm, less than or equal to 5 nm,         less than or equal to 4 nm, less than or equal to 3 nm, less         than or equal to 2 nm or less than or equal to 1.5 nm.

All the configurations according to which the zinc-based metallic layer is located above and not directly in contact with the silver-based functional metallic layer have, for an optimized thickness, a resistivity before heat treatment which is not deteriorated compared to a stack which does not comprise the zinc-based metallic layer.

According to the invention, a non-deteriorated resistivity is understood to mean a variation in resistivity attributable to the presence of the zinc-layer which is not greater than 15%, preferably not greater than 10%.

The configuration according to which the zinc-based metallic layer is located above and separated from the silver-based functional metallic layer by a blocking overlayer appears to give the best results.

The configuration according to which the zinc-based metallic layer is situated above and separated from the silver-based functional metallic layer by a blocking overlayer and a crystallized layer also gives good results.

It is also possible to use a blocking underlayer in these configurations. The use of the blocking underlayer enables an improvement in the mechanical strength. A blocking underlayer located below a silver layer and a zinc-based metallic layer located above and directly in contact with said silver layer, or separated from the silver layer by a crystallized layer and/or by a blocking overlayer, are then combined.

The configurations according to which the zinc-based metallic layer is located below and close to the silver-based functional metallic layer exhibit a deteriorated resistivity before heat treatment. A possible explanation is that the zinc layer under the silver layer increases the roughness of the lower interface of the silver layer. This is observed when the zinc-based metallic layer is located in contact with a silver-based functional metallic layer or is separated from this silver-based functional metallic layer by at least one blocking underlayer.

According to the invention, the term “layer located close to” is understood to mean a layer located, in increasing order of preference, at less than 15 nm, at less than 10 nm, at less than 5 nm, at less than 4 nm, at less than 3 nm or at less than 2 nm from another layer.

The following embodiments are particularly advantageous since they give the best results:

-   -   the zinc-based metallic layer is located close to the silver         layer, and/or     -   the zinc-based metallic layer is separated from the silver layer         by at least one blocking layer,     -   the zinc-based metallic layer is located above the silver layer,     -   the stack comprises a blocking overlayer located directly in         contact with the silver-based functional metallic layer.

The zinc-based metallic layers, in order to be effective, must allow the diffusion of metallic zinc elements toward the silver layer. It is likely that if these zinc layers are separated from the silver layer:

-   -   by one or more excessively thick dielectric layers, for example         excessively thick layers of zinc tin oxide, and/or     -   by one or more dielectric layers having a barrier function, such         as layers of nitrides of silicon and/or of aluminum and/or of         zirconium,         then the diffusion of these metallic zinc elements will be         greatly reduced or even prevented. The zinc-based metallic layer         then becomes ineffective from the point of view of improving the         mechanical properties.

According to the invention, the stack comprises at least one silver-based functional metallic layer.

The silver-based functional metallic layer, before or after heat treatment, comprises at least 95.0%, preferably at least 96.5% and better still at least 98.0%, by weight of silver relative to the weight of the functional layer.

Preferably, the silver-based functional metallic layer before heat treatment comprises less than 1.0% by weight of metals other than silver, relative to the weight of the silver-based functional metallic layer.

After heat treatment, the silver-based functional metallic layer may comprise a proportion of zinc. Measurement of the doping with zinc can be carried out for example by Castaing microprobe analysis (electron probe microanalyzer or EPMA) or by measurement by atom probe tomography.

The thickness of the silver-based functional layer is from 5 to 25 nm.

The stack of thin layers comprises at least one functional layer and at least two dielectric coatings including at least one dielectric layer, so that each functional layer is disposed between two dielectric coatings.

The stack of thin layers can comprise at least two silver-based metallic functional layers and at least three dielectric coatings including at least one dielectric layer, so that each functional layer is disposed between two dielectric coatings.

The stack of thin layers can comprise at least three functional layers and at least four dielectric coatings including at least one dielectric layer, so that each functional layer is disposed between two dielectric coatings.

The invention is not limited to the insertion of a single zinc-based metallic layer. It is obviously possible to have a zinc-based metallic layer close to at least two silver-based functional layers or each silver-based functional layer.

A stack may thus comprise one or more zinc-based metallic layers.

The stack comprising at least two silver-based metallic functional layers can comprise at least two zinc-based metallic layers close to at least two silver-based metallic functional layers.

It is also possible, in stacks with several silver-based functional layers, for each silver-based metallic functional layer to be situated close to a zinc-based metallic functional layer.

The stack is located on at least one of the faces of the transparent substrate.

The term “dielectric coating” within the meaning of the present invention should be understood as meaning that there may be a single layer or several layers of different materials within the coating. A “dielectric coating” according to the invention comprises predominantly dielectric layers. However, according to the invention these coatings can also comprise layers of another nature, in particular absorbent, for example metallic, layers.

It is considered that a “given” dielectric coating is located:

-   -   between the substrate and the first functional layer,     -   between each silver-based functional metallic layer,     -   above the last functional layer (furthest from the substrate).

The term “dielectric layer”, within the meaning of the present invention, should be understood as meaning that, from the viewpoint of its nature, the material is “nonmetallic”, that is to say is not a metal. In the context of the invention, this term denotes a material having an n/k ratio over the whole visible wavelength range (from 380 nm to 780 nm) of equal to or greater than 5. n denotes the real refractive index of the material at a given wavelength and k represents the imaginary part of the refractive index at a given wavelength, the ratio n/k being calculated at the same given wavelength for both n and k.

The thickness of a dielectric coating corresponds to the sum of the thicknesses of the layers constituting it.

The coatings exhibit a thickness of greater than 15 nm, preferably of between 15 and 200 nm.

The dielectric layers of the coatings exhibit the following characteristics, alone or in combination:

-   -   they are deposited by magnetic field-assisted cathode         sputtering,     -   they are chosen from the oxides or nitrides of one or more         elements chosen from titanium, silicon, aluminum, zirconium, tin         and zinc,     -   they have a thickness of greater than 2 nm, preferably of         between 2 and 100 nm.

The dielectric layers may be layers referred to as crystallized layers which are also called “stabilizing layer” or “wetting layer”. The term “stabilizing layer” is understood to mean a layer made of a material capable of stabilizing the interface with the functional layer. These layers are generally based on zinc oxide.

The zinc oxide-based layers can comprise at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99% or 100% by weight of zinc relative to the total weight of all the elements constituting the zinc oxide-based layer excluding oxygen and nitrogen.

In order to be correctly crystallized by cathode sputtering deposition, the zinc oxide-based layers advantageously comprise at least 80%, or at least 90%, by weight of zinc relative to the total weight of all the elements constituting the zinc oxide-based layer excluding oxygen and nitrogen.

The zinc oxide-based layers can comprise one or more elements chosen from aluminum, titanium, niobium, zirconium, magnesium, copper, silver, gold, silicon, molybdenum, nickel, chromium, platinum, indium, tin and hafnium, preferably aluminum.

The zinc oxide-based layers can optionally be doped using at least one other element, such as aluminum.

A priori, the zinc oxide-based layer is not nitrided, however traces may be present.

The zinc oxide-based layer comprises, in increasing order of preference, at least 80%, at least 90%, at least 95%, at least 98% or at least 100% by weight of oxygen relative to the total weight of oxygen and nitrogen.

Preferably, the dielectric coating located directly below the silver-based functional metallic layer includes at least one crystallized dielectric layer, in particular based on zinc oxide, optionally doped using at least one other element, such as aluminum.

In all stacks, the dielectric coating closest to the substrate is called lower coating and the dielectric coating furthest from the substrate is called upper coating. Stacks with more than one silver layer also comprise intermediate dielectric coatings located between the lower and upper coatings.

Preferably, the lower or intermediate coatings comprise a zinc oxide-based crystallized dielectric layer located directly in contact with the silver-based metallic layer or separated by a blocking underlayer.

Preferably, the intermediate or upper coatings comprise a zinc oxide-based crystallized dielectric layer located directly in contact with the silver-based metallic layer or separated by a blocking overlayer.

The zinc oxide layers have a thickness:

-   -   of at least 1.0 nm, of at least 2.0 nm, of at least 3.0 nm, of         at least 4.0 nm, of at least 5.0 nm, and/or     -   of at most 25 nm, of at most 10 nm, of at most 8.0 nm.

The dielectric layers can exhibit a barrier function. Dielectric layers having a barrier function (hereinafter barrier layer) is understood to mean a layer made of a material capable of forming a barrier to the diffusion of oxygen and water at high temperature, originating from the ambient atmosphere or from the transparent substrate, toward the functional layer. Such dielectric layers are chosen from the layers:

-   -   based on silicon and/or aluminum and/or zirconium compounds         chosen from oxides, such as SiO2, nitrides, such as silicon         nitride Si3N4 and aluminum nitrides AlN, and oxynitrides SiOxNy,         optionally doped using at least one other element,     -   based on zinc tin oxide,     -   based on titanium oxide.

Preferably, each coating includes at least one dielectric layer consisting:

-   -   of an aluminum and/or silicon and/or zirconium nitride or         oxynitride, or     -   of a mixed zinc tin oxide, or     -   of a titanium oxide.

Preferably, each dielectric coating includes at least one dielectric layer which has a barrier function and is based on an aluminum and/or silicon and/or zirconium nitride. Preferably, the sum of the thicknesses of all the dielectric layers which have a barrier function and are based on aluminum and/or silicon and/or zirconium nitride in each dielectric coating is greater than or equal to 15 nm, or greater than or equal to 20 nm.

These dielectric layers have, in increasing order of preference, a thickness:

-   -   of less than or equal to 40 nm, of less than or equal to 30 nm,         of less than or equal to 25 nm, and/or     -   of greater than or equal to 5 nm, of greater than or equal to 10         nm or of greater than or equal to 15 nm.

The stack of thin layers can optionally comprise a protective layer. The protective layer is preferably the final layer of the stack, that is to say the layer furthest from the substrate coated with the stack (before heat treatment). These layers generally have a thickness of between 0.5 and 10 nm, preferably 1 and 5 nm. This protective layer can be chosen from a layer of titanium, of zirconium, of hafnium, of silicon, of zinc and/or of tin, this or these metals being in the metal, oxide or nitride form.

According to one embodiment, the protective layer is based on zirconium and/or titanium oxide, preferably based on zirconium oxide, on titanium oxide or on titanium zirconium oxide.

The substrate coated with the stack or the stack alone is intended to undergo a heat treatment. However, the present invention also relates to the non-heat-treated coated substrate.

The stack may not have undergone a heat treatment at a temperature of greater than 500° C., preferably 300° C.

The stack may have undergone a heat treatment at a temperature of greater than 300° C., preferably 500° C.

The heat treatments are chosen from an annealing, for example by rapid thermal annealing (“rapid thermal process”) such as a laser or flash lamp annealing, tempering and/or bending. Rapid thermal annealing is for example described in the application WO2008/096089.

The heat treatment temperature (at the stack) is greater than 300° C., preferably greater than 400° C., and better still greater than 500° C.

The substrate coated with the stack may be a curved or tempered glass.

The transparent substrates according to the invention are preferably made of a rigid inorganic material, for instance made of glass, or are organic, based on polymers (or made of polymer).

The transparent organic substrates according to the invention, which are rigid or flexible, can also be made of polymer. Examples of polymers suitable according to the invention comprise in particular:

-   -   polyethylene;     -   polyesters, such as polyethylene terephthalate (PET),         polybutylene terephthalate (PBT) or polyethylene naphthalate         (PEN);     -   polyacrylates, such as polymethyl methacrylate (PMMA);     -   polycarbonates;     -   polyurethanes;     -   polyamides;     -   polyimides;     -   fluoropolymers, for instance fluoroesters, such as         ethylene-tetrafluoroethylene (ETFE), polyvinylidene fluoride         (PVDF), polychlorotrifluoroethylene (PCTFE),         ethylene-chlorotrifluoroethylene (ECTFE) or fluorinated         ethylene-propylene copolymers (FEP);     -   photocrosslinkable and/or photopolymerizable resins, such as         thiolene, polyurethane, urethane-acrylate or polyester-acrylate         resins; and     -   polythiourethanes.

The substrate is preferably a sheet of glass or of glass-ceramic.

The substrate is preferably transparent, colorless (it is then a clear or extra-clear glass) or colored, for example blue, gray or bronze. The glass is preferably of soda-lime-silica type but it can also be a glass of borosilicate or alumino-borosilicate type.

According to a preferred embodiment, the substrate is made of glass, in particular soda-lime-silica glass, or of a polymeric organic substance.

The substrate advantageously has at least one dimension greater than or equal to 1 m, or 2 m and even 3 m. The thickness of the substrate generally varies between 0.5 mm and 19 mm, preferably between 0.7 and 9 mm, in particular between 2 and 8 mm, or between 4 and 6 mm. The substrate may be flat or curved, or even flexible.

The invention also relates to a glazing comprising at least one material according to the invention. The invention relates to a glazing which can be in the form of monolithic, laminated or multiple glazing, in particular double glazing or triple glazing.

A monolithic glazing comprises 2 faces; face 1 is outside the building and thus constitutes the exterior wall of the glazing and face 2 is inside the building and thus constitutes the interior wall of the glazing.

A multiple glazing comprises at least one material according to the invention and at least one additional substrate, the material and the additional substrate are separated by at least one intermediate gas-filled space. The glazing provides a separation between an exterior space and an interior space.

A double glazing comprises 4 faces; face 1 is outside the building and thus constitutes the exterior wall of the glazing and face 4 is inside the building and thus constitutes the interior wall of the glazing, faces 2 and 3 being inside the double glazing.

A laminated glazing comprises at least one structure of first substrate/sheet(s)/second substrate type. The polymeric sheet can in particular be based on polyvinyl butyral PVB, ethylene/vinyl acetate EVA, polyethylene terephthalate PET or polyvinyl chloride PVC. The stack of thin layers is positioned on one at least of the faces of one of the substrates.

These glazings may be fitted to a building or a vehicle.

These glazings may be fitted to devices such as oven or refrigerator doors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1D are images taken under a microscope of scratches made after indentation with a force of 0.8 or 3 N followed by heat treatment;

FIGS. 2A-2B are optical images and FIGS. 2C and 2D are images taken under a microscope of scratches made after indentation with a force of 3 N followed by heat treatment;

FIGS. 3A-3F are optical images showing the visibility of corrosion after 5 and 20 days of the HH test on non-heat-treated materials (3A, 3B, 3D, 3E) and heat-treated materials (3C and 3F); and

FIGS. 4A-4B are images taken under a microscope showing the defects due to corrosion after 5 days of the HH test before heat treatment (4A) and after heat treatment (4B).

The following examples illustrate the invention.

EXAMPLES I. Preparation of the Substrates: Stacks, Deposition Conditions

Stacks of thin layers defined below are deposited on substrates made of clear soda-lime glass with a thickness of 2 or 4 mm.

In the examples of the invention:

-   -   the functional layers are silver (Ag) layers,     -   the blocking layers are metallic layers made of alloy of nickel         and of chromium (NiCr),     -   the dielectric layers are based on silicon nitride, doped with         aluminum (Si₃N₄:Al) and on zinc oxide (ZnO).

The conditions for deposition of the layers, which were deposited by sputtering (“magnetron cathode” sputtering), are summarized in table 1.

TABLE 1 Deposition Target employed pressure Gas Ag Ag 8 × 10⁻³ mbar 100% Ar Zn Zn 2 × 10⁻³ mbar 100% Ar NiCr Ni:Cr at 80%:20% by 2 × 10⁻³ mbar 100% Ar weight Si₃N₄ Si:Al at 92%:8% by weight 2 × 10⁻³ mbar  55% Ar/(Ar + N₂) ZnO Al:ZnO (5% Al by weight) 2 × 10⁻³ mbar 100% Ar

The tables below list the materials and the physical thicknesses in nanometers (unless otherwise indicated) of each layer or coating which forms the stacks as a function of their positions with regard to the substrate carrying the stack.

Materials Layers Ref. 1 Ref. 2 Stack 1 Stack 2 Dielectric coating Si₃N₄ 30 30 30 30 ZnO 5 5 5 5 Zn — — 2-8 nm 2 Blocking layer OB NiCr 1 1 1 1 Functional layer Ag 10 10 10 10 Blocking layer UB NiCr — 1 — 1 Dielectric coating ZnO 5 5 5 5 Si₃N₄ 20 20 20 20 Substrate (mm) glass

Stack 1 Stack 1-2 Stack 1-4 Stack 1-6 Stack 1-8 Zn thickness 2 nm 4 nm 6 nm 8 nm Materials Layers Ref. 3 Stack 3-1 Stack 3-2 Dielectric coating Si₃N₄ 21 21 21 ZnO 5 5 5 Zn 0 0 2 Blocking layer OB NiCr 1 1 1 Functional layer Ag 18 18 18 Blocking layer UB NiCr 1 1 1 Dielectric coating ZnO 5 5 5 Si₃N₄ 77 77 77 ZnO 5 5 5 Zn 0 2 0 Blocking layer OB NiCr 1 1 1 Functional layer Ag 11 11 11 Blocking layer UB NiCr 1 1 1 Dielectric coating ZnO 5 5 5 Si₃N₄ 36 36 36 Substrate (mm) glass

II. Mechanical Properties

Erichsen scratch tests (ESTs) were carried out under the following conditions:

-   -   EST: This test consists in applying a tip (Van Laar tip, steel         ball) with a given force (in newtons) to produce a scratch in         the stack and possibly to report the width of the scratches. The         EST test (without other qualifier) is carried out without heat         treatment.     -   EST-HT: This test consists in performing an EST test followed by         a heat treatment under the following conditions: Force applied:         0.3 N, 0.5 N, 0.8 N, 1 N, 3 N or 5 N; heat treatment, 10 minutes         at a temperature of 650° C.,     -   HT-EST: This test consists in performing a heat treatment         followed by an EST test under the following conditions: Heat         treatment, 10 minutes at a temperature of 650° C.; force         applied: 0.3 N, 0.5 N, 0.8 N, 1 N, 3 N or 5 N.

The table below shows the results of measuring the width of the scratches in μm with an applied force of 0.8 N.

Stack Stack Stack Stack HT-EST 0.8N Ref. 1 1-2 1-4 1-6 1-8 Scratch width 18 13 11 16 21 (μm)

The HT-EST test shows that the depth of the scratches decreases gradually as the zinc thickness increases from 2 to 4 nm, before increasing again when the zinc thickness is between 6 and 8 nm.

The material comprising 4 nm of zinc leads to the greatest scratch resistance from the viewpoint of scratch width and scratch visibility. These results are observed for both the HT-EST test and the EST-HT test.

The improvement provided by the zinc in the decrease in the width of the scratches is significant between 2 and 4 nm in view of the examples. In alternative embodiments, an improvement could be observed for lower metallic zinc thickness ranges.

The EST-HT and HT-EST tests were also carried out on Ref. 2 and Stack 2, which differ from Ref. 1 and Stack 1-2 by the presence of a blocking underlayer. These tests show similar results, that is to say that the use of a 2 nm zinc-based metallic layer leads to a significant improvement in mechanical properties, reflected by a decrease in the width of scratches and in the visibility of scratches.

III. Microscopic Observations: Hot Corrosion

a. Stacks with a Single Functional Layer

The morphology of the layers is analyzed by optical microscopy. Images of the scratches were taken after test EST-HT (EST at 0.8 or 3 N followed by a heat treatment at 650° C.

FIGS. 1 -a, 1-b, 1-c, 1-d are images taken under a microscope of scratches made after indentation with a force of 0.8 or 3 N followed by heat treatment.

EST-HT 0.8N EST-HT 3N Image Width Image Width Ref. 1 1-a 25-35 1-b 40-60 Stack 1-2 1-c  0-10 1-d  0-15

The scratches, when they are present, are much thinner for the material according to the invention than for the reference material. But most significantly, the scratches in the materials according to the invention comprising a zinc-based metallic layer are not corroded at all.

These observations clearly show that the incorporation of the metallic zinc performs two functions. It improves the scratch resistance but also drastically improves the resistance to hot corrosion.

Lastly, the images after EST-HT clearly suggest that no scratches would be observed after an EST test at 0.8 and 3 N. This means that the presence of the metallic zinc layer located above the silver layer has not altered the scratch resistance before heat treatment.

b. Stacks with Several Functional Layers

FIGS. 2 -a and 2-b are optical images and FIGS. 2 -c and 2-d are images taken under a microscope of scratches made after indentation with a force of 3 N followed by heat treatment.

EST-HT 3N Images Width Ref. 3 2-a and 2-c 120-160 Stack 3-1 2-b and 2-d  0-30

These images clearly show the drastic reduction in scratches as a result of the solution of the invention.

The microscope observations show that the scratches made before heat treatment become highly corroded following the heat treatment for the reference example Ref. 3. In comparison, the use of a zinc-based metallic in Stack 2-1 according to the invention makes it possible to almost entirely eliminate any hot corrosion (FIG. 2 -d).

It is also observed for the material of the invention that the width of the scratches before heat treatment (EST) is lower than for the reference example. This shows that the solution of the invention also makes it possible to reduce the scratch resistance before heat treatment.

EST-HT tests were carried out for Stack 3-2. The results are similar to those obtained with Stack 3-1.

Consequently, in a stack with several silver layers, a positive effect is observed for the insertion of a zinc-based metallic layer when this layer is positioned anywhere close to just one of the silver layers.

However, the invention is not limited to the insertion of a single zinc-based metallic layer. It is obviously possible to have a zinc-based metallic layer close to at least two silver-based functional layers, or even each silver-based functional layer.

IV. Microscopic Observation: Cold Corrosion

High-humidity tests (HH tests) were carried out. These tests consist in placing the materials at 90% humidity and at 50° C. for 5 and 20 days. The materials tested are Ref 1 and Stack 1-2.

The tests were carried out on non-heat-treated materials (BT) and on heat-treated materials (AT). The table above indicates whether sites of corrosion (Corr. sites) are observed. The following ratings are given:

-   -   “0”: no corrosion sites,     -   “+”: some corrosion sites,     -   “++”: visible corrosion sites,     -   “+++”: many corrosion sites.

FIG. 3 comprises optical images showing the visibility of corrosion after 5 and 20 days of the HH test on non-heat-treated materials (3-a, 3-b, 3-d, 3-e) and heat-treated materials (3-c and 3-f).

FIG. 4 comprises images taken under a microscope showing the defects due to corrosion after 5 days of the HH test before heat treatment (4-a) and after heat treatment (4-b).

5 days BT 20 days BT 20 days AT HH Corr. Corr. Corr. test Image sites Image sites Image sites Ref. 1 3-a, 4-a + 3-b ++ 3-c +++ BT Stack 3-d 0 3-e 0 3-f + 1-2 BT BT: Before heat treatment, AT: After heat treatment, “—”: no image.

The reference stack without heat treatment exhibits corrosion defects visible to the eye after 5 days of the HH test (FIGS. 3 -a and 4-a). The density of the corrosion sites increases after 20 days of the HH test (FIG. 3 -b).

For the materials according to the invention without heat treatment, the presence of a zinc-based metallic layer prevents the formation of corrosion sites (FIGS. 3 -d and 3-e). No corrosion sites are observed after 5 days and only a few sites are observed after 20 days.

The incorporation of a zinc-based metallic layer significantly increases the resistance to cold corrosion.

The heat-treated reference stack becomes completely hazy after 20 days (FIG. 3 -c). Characterization under an optical microscope after 5 days (FIG. 4 -b) shows a very high density of micrometric defects in addition to the wide corrosion defects already observed for the non-heat-treated material (FIG. 4 -a).

For the heat-treated materials according to the invention, the presence of a zinc-based metallic layer prevents the formation of haze associated with cold corrosion (FIG. 3 -f).

According to the invention, by virtue of the incorporation of a zinc-based metallic layer, a significant improvement in the resistance to cold corrosion is observed both in heat-treated and non-heat-treated materials.

V. Evaluation of the Deterioration in the Resistivity and the Absorption

1. Influence of the Thickness of the Zinc Layer and of the Temperature of the Heat Treatment

The sheet resistance Rsq, corresponding to the resistance related to the surface area, is measured by induction with a Nagy SMR-12 instrument. The sheet resistance was measured before heat treatment (BT) and after heat treatments at temperatures ranging from 300 and 650° C. for 10 min (AT).

The table below shows the results for sheet resistance (values given in ohm/□) and for absorption (abs.) obtained for coated substrates, before and after tempering, as a function of the thickness of the zinc-based metallic layer.

Stack Stack Stack Stack Stack Ref. 1 1-2 1-4 1-6 1-8 Rsq before HT 5.9 6.5 8.9 10.2 11.7 Rsq after 300° C. HT 5.5 7.3 11.9 14.2 15.3 Rsq after 650° C. HT 4.4 6.9 10.0 11.4 12.5 Abs. after 650° C. HT 10% 14% 22% 28% 34%

It is observed that Stack 1-2, comprising a metallic zinc layer thickness of 2 nm, exhibits non-deteriorated resistivity, that is to say a variation in resistivity attributable to the presence of the zinc layer of less than 9%.

The reference stack (without metallic zinc layer) exhibits a reduction in its resistivity following the heat treatment which is proportional to the temperature of the heat treatment. This improvement in resistivity is equal to approximately 10 and 30% at 300 and 650° C., respectively.

When a zinc-based metallic layer is added, the improvement in resistivity following the heat treatment decreases gradually with increasing zinc thicknesses.

The resistivity deteriorates starting from 300° C., compared to the reference example. At 650° C., the resistivity has deteriorated but less significantly so than at 300° C.

The absorption increases gradually with zinc thickness (Stacks 1-2 to 1-8 and Ref. 1).

2. Influence of the Presence of an Underblocker Layer

The sheet resistance and the absorption were measured before heat treatment (BHT) and after heat treatments at a temperature of 650° C. for 10 min (AHT).

a. Stacks with a Single Functional Layer

The variation in resistivity is determined in the following way: ΔRsq_((AT vs. BT))=(Rsq_(AT)−Rsq_(BT))/Rsq_(BT)×100.

Rsq (Ω/□) ΔRsq (%) Abs (%) Material BT AT (AT vs. BT) BT AT Ref. 1 6.3 4.4 +30 11 7 Stack 1-2 6.9 7.6 −10 19 12 Ref. 2 7.3 4.6 +37 14 9 Stack 2 8.1 7.8 +4 22 16 BT: Before heat treatment, AT: after heat treatment.

When the stack does not comprise an underblocker layer and comprises a zinc layer (Stack 1-2), the sheet resistance is deteriorated after heat treatment, while the reference stack 1 without zinc layer exhibits an improvement of 31% after heat treatment.

Reference example 2 comprising a blocking underlayer and not comprising a zinc layer exhibits an improvement of 37%.

When the stack comprises an underblocker layer and comprises a zinc layer (Stack 2), an improvement in resistivity of 4% is observed. The resistivity thus deteriorates significantly less during the heat treatment when the stack comprises a blocking underlayer. In the presence of a blocking underlayer, the incorporation of a zinc-based metallic layer thus has a less severe impact on the resistivity after heat treatment.

This trend suggests that metallic zinc species partially diffuse during the heat treatment at the lower interface of the silver layer and deteriorate the resistivity. Given that this lower interface has already deteriorated due to the presence of the blocking underlayer, the diffusion of metallic zinc species has an adverse effect on the resistivity, though to a lesser extent than in the case where there is no blocking underlayer.

b. Stacks with Several Functional Layers

Rsq (Ω/□) ΔRsq_((AT vs. BT)) Abs (%) Materials BT AT (%) BT AT Ref. 3 1.95 1.44 26 30 19 Stack 3-1 1.98 1.56 21 35 24 Stack 3-2 1.98 1.74 12 35 24

The reference stack (Ref. 3) exhibits a conventional improvement in resistivity after heat treatment, of 26%. The stacks according to the invention comprising a zinc layer exhibit respective improvements in resistivity after heat treatment of 21 and 12%.

The greater deterioration in the resistivity observed for the stack Stack 3-2 can be explained by the fact that the thickness of Ag-2 (18 nm) is greater than that of Ag-1 (11 nm). However, it can be noted that, overall, the resistivity deteriorates significantly less than what is generally observed for stacks not comprising a blocking underlayer.

The reason for the lower deterioration in resistivity induced by the incorporation of a zinc-based metallic layer is attributable to the presence of the blocking underlayer, as explained above.

An increase in the absorption from 19% to 24% is observed when a zinc layer is added.

VI. Conclusion

The examples according to the present invention show that the insertion of a zinc-based metallic layer drastically improves the mechanical properties, with in particular a reduction in the visibility of scratches before and after heat treatment (EST, EST-HT and HT-EST test results). The incorporation of the zinc-based metallic layer also results in a great reduction in the hot corrosion, indeed even the elimination thereof as proven by the results of the EST-HT test.

The solution of the invention thus makes it possible to:

-   -   obtain an excellent scratch resistance,     -   significantly improve the resistance to hot corrosion,     -   significantly improve the resistance to cold corrosion.

On the other hand, the use of such a layer has an impact on the resistivity and the absorption. The use of a blocking underlayer makes it possible to reduce the deterioration in the resistivity. 

The invention claimed is:
 1. A material comprising a transparent substrate coated with a stack of thin layers comprising at least one silver-based functional metallic layer and at least two dielectric coatings, each dielectric coating including at least one dielectric layer, so that each silver-based functional metallic layer is disposed between two dielectric coatings, wherein the stack comprises, in the following order starting from the substrate: a first silicon nitride layer; a first crystallized zinc oxide layer in contact with the first silicon nitride layer and having a first thickness from 1.0 nm to 8.0 nm; a silver-based functional metallic layer in contact with the first crystallized zinc oxide layer or separated from the first crystallized zinc oxide layer by a blocking underlayer having a thickness from 0.1 nm to 5.0 nm; a nickel chromium-based metallic layer in contact with the silver-based functional metallic layer and having a thickness from 0.1 nm to 5.0 nm; a zinc-based metallic layer in contact with the nickel chromium-based metallic layer; a second crystallized zinc oxide layer in direct contact with the zinc-based metallic layer and having a second thickness from 1.0 nm to 8.0 nm, and a second silicon nitride layer in contact with the second crystallized zinc oxide layer, wherein a total thickness separating the first silicon nitride layer from the silver layer is from 1 nm to 13 nm.
 2. The material as claimed in claim 1, wherein the nickel chromium-based metallic layer in contact with the silver-based functional metallic layer has a thickness of between 0.1 and 2.0 nm.
 3. The material as claimed in claim 1, wherein a thickness of the zinc-based metallic layer is from 0.2 to 10 nm.
 4. The material as claimed in claim 1, wherein the zinc-based metallic layer comprises at least 20% by weight of zinc relative to the weight of the zinc-based metallic layer.
 5. The material as claimed in claim 1, wherein the first crystallized zinc oxide layer is optionally doped using at least one other element.
 6. The material as claimed in claim 1, wherein the stack has not undergone a heat treatment at a temperature of greater than 500° C.
 7. The material as claimed in claim 1, wherein the stack has undergone a heat treatment at a temperature of greater than 300° C.
 8. The material as claimed in claim 1, wherein the substrate is made of glass or of a polymeric organic substance.
 9. A glazing comprising a material as claimed in claim 1, wherein the glazing is in the form of monolithic, laminated or multiple glazing.
 10. The material as claimed in claim 1, wherein the stack comprises said blocking underlayer.
 11. The material as claimed in claim 6, wherein the stack has not undergone a heat treatment at a temperature of greater than 300° C.
 12. The material as claimed in claim 7, wherein the stack has undergone a heat treatment at a temperature of greater than 500° C. 